[Stoves] Two Stove System - typos corrected v1.1

[Frank Shields]

Dear Crispin,

Thanks and I like everything you say. 

But one comment based on the paragraph below I copied and brought to the top.:

The problem I have is all the estimates for values that are being used. I hope that will end when stoves start to be tested in labs. Also; if we are talking Fuel Efficiency for Task 1 then what we (he people) want to know is how much fuel will be used for completing a task. So I would say the joules is a proxy for the fuel and a proxy for the task - not the other way around.  

And there is a lot more to know about fuel than joules per mass. 

And if you do use LHV how do you plan to determine what that is? You will need to test for hydrogen. If you plan to guess with a typical value I suggest using HHV. Using HHV will eliminate a lot of lab work and expensive equipment. Using a value from a guess is already an error happening. Same as what is happening with moisture. Suggest adjusting moisture to an agreed upon value and letting it do what it is going to do. Use dry wt as your energy value. A good stove will make good use of that moisture and show in the results. A poor designed stove will be robbed of heat and that will show. Another guess that should be avoided IMO. 

Thanks

Frank





> There is no gain in turning things into a mass of fuel – different fuels have different energy contents. Stay away from fuel mass! Fuel mass if a proxy for energy. Just use the energy because all the fuels contain potential combustion energy so there is a common metric (Joules). Use the common metric.  Using fuel mass, everyone would have to use the same fuel in order to compare stoves, which is not realistic or wise. Changing the fuel type changes the performance so the testing context has to reflect what people do. 






> On Nov 29, 2015, at 12:16 AM, Crispin

> Pemberton-Pigott <crispinpigott at outlook.com> wrote:
> 
> >Two more quick questions: 
>  
> >Is moisture still in the calculations? and 
> >is this HHV or LHV?
>  
> The energy available from the fuel is based on the actual LHV available considering the fuel moisture content.
>  
> >Just one more question:
>  
> >If our only task was making tea then measuring the energy going into the water would be easy. But the efficiency of cooking our rice would be much harder. 
>  
> Actually it is not difficult to determine the efficiency of a stove cooking rice. The actual cooking of rice can be performed and the stove observed. Then reproduce the cooking cycle with water in the pot, without rice. If it is really necessary to work out the energy used for a particular food, there are tables of energy absorbed by different foods. What food happens to be in a pot does not affect the ability of a stove to create heat from fuel and transfer it, fortunately. The stove operates independently of what is in the pot.
>  
> >And grilling our meat would be very hard. 
>  
> There is no real need to get the heat gained by a pot during a particular meal. People cook more than one meal so a proxy cooking cycle incorporating various behaviours – average behaviour – can be used. It an investigation is made into the average behaviour of a family, a community or a region, one can get various cycles that represent ‘average behaviour’. That is the best we can do. There is no need (or intention) to predict the performance of any particular meal in the field.  What is good however, is to be able to reasonably predict performance in a given community or performing a given task like making sugar or drying fish. A stove can be tuned to that purpose. 
>  
> A variety of proxy cooking tasks can be used in the lab representing various behaviours. For roasting meat, it comes down to reproducing the fire pit and duration. You can rate the performance in terms of ‘producing cooked meat mass’ but not the heat received by the meat. There is no need to do that. If you were drying fish you could rate the production per hour or per day. That is no thermal efficiency number available from that, but you could get an energy consumption per kg of fish, based on the energy content of the fuel consumed per day.
>  
> Therefore I am wondering why you done have energy from the fuel (that can always easily be normalized to the actual fuel mass used) per specific task completed? 
>  
> There is no gain in turning things into a mass of fuel – different fuels have different energy contents. Stay away from fuel mass! Fuel mass if a proxy for energy. Just use the energy because all the fuels contain potential combustion energy so there is a common metric (Joules). Use the common metric.  Using fuel mass, everyone would have to use the same fuel in order to compare stoves, which is not realistic or wise. Changing the fuel type changes the performance so the testing context has to reflect what people do. 
>  
> As a result of performing a test in a particular context (to get a prediction of performance in use) the performance has to be stated together with the testing conditions. There is no ‘clever’ way around this, however much we wish it to be so. An example of this fact can be observed in that the species of wood affects the rate of char production even if everything else is the same. So a stove can’t have a ‘certain’ char production rate. A number has to be attached to a species and its moisture content. A stove could be optimised to deal with a particular input fuel so generalisations are not possible.
>  
> Regards
> Crispin
>  
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